In oil field operations, there are many oil fields at remote locations where the accumulated oil production can be stolen by the operation of a control valve on the oil storage tank. Such theft of oil is a well known and common problem and heretofore there has been no effective simple way of preventing unauthorized operation of flow control valves in an oil field operation.
A lock for a fuel line valve is shown in U.S. Pat. No. 4,420,314.
In the present invention, lock means are provided which are attachable to an oil field valve and have dual keyed control means for access control thus preventing unauthorized operation of an oil field valve.